The investigators hypothesize that a complex combination of regulatory mechanisms is responsible for the low level of EGFR expression in ER+ breast cancer cells and that alterations in these mechanisms results in EGFR up- regulation during the progression to hormone-independence, and ultimately the overexpression of EGFR in ER- breast cancer cells. Using the available molecular biological techniques and the resources of the Lombardi Cancer Center, the investigators proposed to study three specific aims: 1) to determine the mechanisms by which low basallevels of EGFR are maintained in ER+ breast cancer cells, 2) to determine the mechanisms by which overexpression of EGFR occurs in ER- breast cancer cells and 3) to define the role of EGFR in the progression of breast cancer to hormone-independence. The results of the study may provide a specific target for the treatment and prevention of hormone-independent breast cancer.